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It's shock damage. I once heard tell that they always shipped LP's with the Rhythm/Treble switch knob off, because the same would happen to them. That was probably bakelite or similar though, before plastics.

It's shock damage. I once heard tell that they always shipped LP's with the Rhythm/Treble switch knob off, because the same would happen to them. That was probably bakelite or similar though, before plastics.

From the usual source:
"Bakelite was designated a National Historic Chemical Landmark on November 9, 1993, by the American Chemical Society in recognition of its significance as the world's first synthetic plastic.[4]"
Ok to be fair plastic's a very generic term and truth to tell, my aging memory had Bakelite confused with Henry Ford's soybean based plastic.
For sure Bakelite's pretty brittle stuff though, and I get what you mean, the way those knobs compressed and sheared without actually breaking (and are clear) probably indicate a polycarbonate plastic.
On reflection wouldn't surprise me if vintage Gibson knobs were actually NC-based plastic (celluloid) like was used for bindings in the '50's and which breaks down over time becoming very fragile.

From the usual source:
"Bakelite was designated a National Historic Chemical Landmark on November 9, 1993, by the American Chemical Society in recognition of its significance as the world's first synthetic plastic.[4]"
Ok to be fair plastic's a very generic term and truth to tell, my aging memory had Bakelite confused with Henry Ford's soybean based plastic.
For sure Bakelite's pretty brittle stuff though, and I get what you mean, the way those knobs compressed and sheared without actually breaking (and are clear) probably indicate a polycarbonate plastic.
On reflection wouldn't surprise me if vintage Gibson knobs were actually NC-based plastic (celluloid) like was used for bindings in the '50's and which breaks down over time becoming very fragile.

I think he means the old knobs were bakelite - not the ones on my guitar.

GAD, I have 8 of those knobs. Two are stripped though and move freely on the shaft. I don't think I will ever put them back on my Blues 90 or Bluesbird as they feel cheap compared to other options out there. Let me know if you are interested. I will have to go find them... I want to say one set is slightly yellowed and the other is clear.

I think he means the old knobs were bakelite - not the ones on my guitar.

Right.
I was addressing this comment:
"That was probably bakelite or similar though, before plastics "
And probably should have bolded it to make that clear in my post.
Suspect the modern stuff's polycarbonate plastic.